1. Technical Field
The invention relates generally to stress memory techniques, and more particularly, to a method of providing a dual stress memory technique and related structure.
2. Background Art
The application of stresses to field effect transistors (FETs) is known to improve their performance. When applied in a longitudinal direction (i.e., in the direction of current flow), tensile stress is known to enhance electron mobility (or n-channel FET (nFET) drive currents) while compressive stress is known to enhance hole mobility (or p-channel FET (pFET) drive currents).
One manner of providing this stress is referred to as stress memorization technique (SMT), which includes applying an intrinsically stressed material (e.g., silicon nitride) over a channel region and annealing to have the stress memorized in, for example, the gate polysilicon or the diffusion regions. The stressed material is then removed. The stress, however, remains and improves electron or hole mobility, which improves overall performance. The anneal is typically provided as part of a dopant activation anneal.
One problem with SMT is that it is applicable only to n-type field effect transistors (nFETs). In particular, while a compressively stressed silicon nitride layer can be formed over a pFET to impart a compressive stress, the stress is removed for the most part by the subsequent and requisite dopant activation anneal. That is, most of the compressive stress is not memorized in the pFET.
In view of the foregoing, there is a need in the art to provide SMT for both nFETs and pFETs.